Method for developing copies using electrophotographic layers



United States Patent 8 Claims. Z01. 96-1) This invention relates to amethod for developing copies using electrophotographic layers by meansof a heating effect after producing a latent image in theelectrophotographic layer. The invention further relates to a materialfor carrying out this method.

It is known to charge an electrophotographic layer in an electric fieldand to produce a charge distribution corresponding to the original inthis layer by exposure. This charge distribution forms a latent image inthe layer. For developing this latent image, the layer is dusted with apigment powder which adheres to the layer according to the dimensions ofthe charge distribution corresponding to the latent image. For fixing,the pigment powder is fused. This method on the one hand requires aconsiderable expenditure on equipment and furthermore has thedisadvantage that the distribution of the developer powder can only bepoorly controlled. Furthermore, the developer powder dust spreads to allparts of the ap paratus so that, if no special protective precautionsare taken, the efficiency of the apparatus is reduced. In addition, itis comparatively difficult to spread the powder in uniform consistency.

For avoiding the latter difficulty, recourse has been had to theso-called wet development, in which the surface carrying theelectrostatic image is exposed to a liquid developer having a liquidphase of electrical resistance so high that disiniegration of the latentimage is prevented, in which a pigment, which is electrically selectivewith respect to the image charge, is dispersed, and which includes acontrol material making the pigment electrically selective. In thisprocess, the liquid phase must then be evaporated. For the applicationof the liquid and for the evaporation thereof, further special equipmentis necessary, protective measures for the parts of the apparatus whichare not of use in the evaporation steps being necessitated by theevaporation. In addition, in this latter melhod the original advantageof a dry development is lost.

The invention is based on the problem of providing a method and materialwhich, using latent charge images in a dry process, enable developmentand if required fixing without the disadvantages of the known processes.

This problem is solved in that the electrophotographic layer is exposedto a source of heat radiation and that a heat distribution correspondingto the latent image is produced in this layer and in that this layer isexposed to said heat radiation when in engagement with heat-reactivedeveloping material, i.e. material which reacts or dissolves at a fixedtemperature, whereby the material melts in accordance with the latentimage and forms a visible image.

One feature of the invention lies in that the latent charge image of anelectrophotographic layer has, in particular for heat rays of longwavelengths such as infrared rays, a (heat) conductivity different fromthat of the layer outside the image or without image representation.

The expression electrophotographic layer relates to materials which canordinarily be used in electrophotographic processes. Advantageously, thecoated backings which have been employed previously inelectrophotographic processes can be used as the electrophotographiclayer. According to an advantageous embodiment of the 3,234,l8 PatentedFeb. 8, 1966 "ice invention, developer materials in combination with aheatreactive material are provided on the electrophotographic sheet withthe electrostatic latent image and are exposed to heat rays.

Advantageously, the developer substances are arranged on a separatebacking, which is first brought into contact with theelectrophotographic layer after the production of the electrostaticimage and then has the heat ray applied thereto. This contact isadvantageously effected under pressure, the layer and the backing withthe developer substances for example being pressed together inframe-like supports.

The invention includes the provision of developer materials which, at afixed temperature, carry out chemical and/or physical reactions inaccordance with the dimensions of the electrostatic latent image.

In the preferred embodiment of the invention, which uses a specialbacking for the developer substances, a known developer powdercomprising pigment materials is uniformly distributed on the backing bymeans of a fusible means such as a wax or a low melting resin which mayhave a colophony base. For carrying out this process, the backing isexposed to a heat ray when the developer substance on the specialbacking has been brought in contact with the electrophotographic sheetin which the electrostatic latent image is located, the developer layerside of the special backing lying against the electrophotographic sheet.Advantageously, the heat ray is applied from the side of theelectrophotographic sheet which latter in this manner acts as aselective heat filter.- This process has the advantage that the fixingis carried out in the same step as the developing since the pigmentparticles of the developer which are set free in the region of theelectrostatic latent image by liquification of the fusible substance arefused to the electrophotographic sheet. After a sufficient period oftime of heat ray application a visible image has been formed on thebacking. This visible image corresponds to the latent image in theelectrophotographic layer. Thereupon the electrophotographic layer isseparated from the backing which carries said visible image.

An infra-red source is advantageously used for producing the heat ray.It is pointed out, however, that the rays from the heat source may havewavelengths between from the end of the visible light to and includingthe infrared region.

Within the scope of the above embodiment, the invention includes the useof developer substances on a special backing, whereby the developersubstances are released by a heating effect at a fixed temperature, aretransferred to the electrophotographic layer in accordance with thedimensions of the electrostatic latent image therein and are fixed onthis layer.

According to a different embodiment, developer substances are used whichunder the effect of heat rays of a fixed temperature carry out a col-ourchange on the special backing for the developer substances and/or withmaterials on the electrophotographic layer.

It is pointed out that the use of a selective heat filter in the form ofan electrostatic latent image ensures the accurate reproduction of theoriginal independently of colour variations on the original.

The developer material for carrying out this process contains, in oneembodiment, pigment materials in uniform distribution in a fusiblesubstance on a backing. As fusible substances are used waxes, forexample paraffin wax or ceresin wax, which are particularly stable andhave, for example, a melting point between 60 and C. The inventionincludes as fusible substance resins having low melting points, forexample of colophony basis.

As pigment material, carbon black is advantageously used in the aboveembodiment. Also within the scope of-tne invention lies the use ofdeveloper materials with accurately defined melting points and whichhave been previously used in electrophotographic processes,advantageously those powders being used which have the lowest possiblemelting point. As an example, the developer material may comprise acombination of substantially 15% carbon black and substantially 85% ofso-called highest wax type S with a melting point of about 80 C. Thisdeveloper material is applied to a paper, for example of low quality.

According to a further example, the developer layer applied to thesecond backing has the composition quoted below.

In this connection, there is referred to a backing which afterexposureof the; photoconductive layer or the photoconductive layerbacking, if this layer is arranged on a special backing, is exposed toheat rays while being pressed against the photoconductive layer orphotoconductive layer backing.

Composition of developer layer I grammes Wax KP 2 grammes emulsifier2106 10 ml. paraffin oil 100 ml. distilled water 2 grammes potash 3grammes special black dye IV In the foregoing the chemical nomenclaturefor the trade names used for the several components is as follows:

Special black dye IV is a product of Degussa containing 89% C, 1.1% H,.7% N, .3% S, and 8.9% 0.

According to the Fiat Final Report No. 737 of March 8, 1946, page 14,the wax type S is produced by a chrom acid oxidation of raw montan waxand is composed of- 80% by weight of wax acid and 15 to by weight of theoriginal wax ester.

The same Fiat Final Report No. 737 on page 19 discloses the productionof Wax KP by an esterification of a wax acid produced from raw montanwax by meansof a chrom acid oxidation with multivalent alcohols.

The Emnlsifier 2106 is an organic substance emulsifiable in water andcomposed of a mixture of different polyglycol-ether as disclosed in theGerman patent specification No. 1,020,426.

Special black dye IV is generally used for printing and copying inks,dye bands, carbon papers and lacquers, and

its composition is about Percent Carbon (C) 89.0 Hydrogen (H) 1.1Nitrogen (N) 7.0 Sulphur (S) 3.0 Oxygen (O) 8.9

It is pointed out that in each case the photoconductive layer is'advantageously sheet-shaped, being arranged on a special carrier orbeing self-supporting.

For carrying out the invention, there is furthermore proposed a materialwhich comprises a chemical sheet on a backing, on which sheet the stableparts efiect a colour change above a fixed temperature. Using thismaterial, the developed image is produced on the back-,

4. 7 ing of this material, while the electrophoto'graphic layer can beagain used after dischargingand .a new charging. The process accordingto the invention has substantial advantages. quired fixing :in a dryprocess only comparatively simple apparatus with a heat ray source isrequired, which in addition can easily be combined with a known exposuredevice. Furthermore, the handling of the developer substances, inparticular in comparison with the developer powder used .inelectrophotographic processes, is considerably simplified. In thisconnection, ittis to be noted that the storage ability is improved,since the greatest,

independence from environmental influences from. the

point of view of normal temperature and humidity variations exists.

In addition, the production of the vbacking having the developersubstance layer is considerably. simpler than V the productioniof thepreviously used developer powder which requires specialcarrierparticles.

What I claim is:

1. The method of making a copy from an electrostatic latent imageproduced inran electrophotographiclayer,

in which the ,ele'ctrophotographic layer is brought into contact. bypressure with a second layer containing developer substances whichwhensubjectedto heat. react with said electrophotographic-layer and thelatent image said second layer which lattercarries now a visible image-2. Av method as claimed in claim 1, in which the.

second layer 'contains developi-ng materials which on being heated byinfra-red rays carry out reactions according to the latent image andproduce the'visible image in thesecond layer.

3.v A method as claimed in claim 1, in which the' second layer containsdeveloping substances which on being heated by infra-red rays carry outreactions according to the latent image and produce the visible image inthe second layer, said developing substances carry out chemicalreactions and react with substances in said? electrophotographic layer.

4. A method as claimed in claim 1, inwhich the 1 second layer. containsdeveloper substances which on being heated by infra-red rays carry outreactions according to the latent image and produce the visible image inthesecond lay-en said second layer containing substances, which carryout a color change, at a fixed temperature and (react in dependence withthe degree of heat transfer caused by the heat. conduction of the:electrophotographic layer.

5. A. method as claimed {in claim '1, in which the second layer isapplied to a backing.

6; A method asv claimed in claim 1,2 in which said V the layer sideofthis backing is brought into contact with the electrophotographic layer,whereby upon application of said heat rays said fusible means :meltsaccording/to the electrostatic latent image and the pigment powder, istransferred to theielectrophotographic, layer, adheres thereto and isfixed on this layer by the: action of said heat rays.

'7. A method as, claimedin claim 1, in which said i source of heat raysis applied vfrom the side of the electrophotographic' layer.

8. A method as claimed in claim 1, in which said source, of heat. raysconsists of rays 'in the region at the end of the visible light,including infra-red rays.

(References on following page) By carrying out the development'and ifre- References Cited by the Examiner OTHER REFERENCES UNITED STATESPATENTS Ahsmann et 211.: Applied Scientific Research, v01. A2, 2,297,5910 19 '2 3 1 1950, PP- 2 503 758 6 2 Allen: Electric Stress and HeatTransfer, Brit. 1. 2 629 671 2 1953 Murray 0 425 5 Appl. Physics, V01.10, August 1959, pp. 347-351. 2 692 178 10/1954 G d d g r Marco et a1.,ASME Paper 63-HT-9, published by 2 764 693 9/1956 J b Amer. Soc. ofMech. Eng., 345 E. 47th St., New York, 2,798,959 7/1957 Moncrieff-Yeates96-1 August 1963- g ggg 10 J. TRAVIS BROWN/101mg Primary Examiner.3,010,883 11/1961 Johnson et a1 20418 P IHL P E- MANGAN, Examiner.3,055,906 9/1962 Dreyfios at GERALD BIORGE, ARTHUR L. LIBERMAN,

3O83117 3/1963 Schmiedel et 96 1 C. E. VAN HORN, Assistant Examiners.

1. THE METHOD OF MAKING A COPY FROM AN ELECTROSTATIC LATENT IMAGEPRODUCED IN AN ELECTROPHOTOGRAPHIC LAYER, IN WHICH THEELECTROPHOTOGRAPHIC LAYER IS BROUGHT INTO CONTACT BY PRESSURE WITH ASECOND LAYER CONTAINING DEVELOPER SUBSTANCES WHICH WHEN SUBJECTED TOHEAT REACT WITH SAID ELECTROPHOTOGRAPHIC LAYER AND THE LATENT IMAGETHEREIN, EXPOSING SAID CONTACTING LAYERS TO A SOURCE OF HEAT RAYS TOPRODUCE SAID REACTION IN SAID SECOND LAYER, WHEREBY SAID DEVELOPERSUBSTANCES BECOME ACTIVE IN ACCORDANCE WITH THE DIFFERENTIAL HEATCONDUCTIVITY THROUGHOUT SAID ELECTROPHOTOGRAPHIC LAYER IS DETERMINED BYTHE LATENT IMAGE THEREIN SO AS TO FORM A COPY OF THE LATTER, AND THENSEPARATING SAID ELECTROPHOTOGRAPHIC LAYER FROM SAID SECOND LAYER WHICHLATER CARRIES NOW A VISIBLE IMAGE.